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Question
With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.
Solution
After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac.
A mature embryo sac of angiosperm
Six of the eight nuclei are surrounded by cell walls and organised into cells. Three cells present towards the micropylar end grouped together, constitute the egg apparatus. The egg apperatus, in tum consists of two synergide and one egg cell. Three cells of the chalazal end are called the antipodals. The large central cell is formed by the fusion of 2-polar nuclal. Thus, a typical angiospermic embryo sac, at maturity consisis of eight nuclei and seven cells. This embryo sac is formed from, the single megaspore, so it is called monosporic embryo sac.
Role of synergids
The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid.
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RELATED QUESTIONS
From among the sets of terms given below, identify those that are associated with the gynoecium.
From the statements given below choose the option that are true for a typical female gametophyte of a flowering plant.
- It is 8-nucleate and 7-celled at maturity
- It is free-nuclear during the development
- It is situated inside the integument but outside the nucellus
- It has an egg apparatus situated at the chalazal end
The embryo sac is ______
In an embryo sac, the cells that degenerate after fertilisation are ______.
In a flower, if the megaspore mother cell forms megaspores without undergoing meiosis and if one of the megaspores develops into an embryo sac, its nuclei would be ______.
Draw the diagram of a mature embryo sac and show its 8-nucleate, 7-celled nature. Show the following parts: antipodals, synergids, egg, central cell, polar nuclei.
Embryo sacs of some apomictic species appear normal but contain diploid cells. Suggest a suitable explanation for the condition.
Trace the development of a megaspore mother cell to the formation of a mature embryo sac in a flowering plant.
Explain the monosporic development of the embryo sac in the ovule of an angiosperm.
Draw a diagram of the mature embryo sac of an angiospermic ovule and label any four parts in it.
